Heater partial exhaust gas, recirculating means for relief of pulsations



Jan. 18, 1955 G. J. FAIRBANKS 2,699,818 HEATER PARTIAL EXHAUST GAS, RECIRCULATING MEANS FOR RELIEF OF PULSATIONS Filed Aug. 29, 1950 el e j l 5I i United States Patent O HEATER PARTIAL EXHAUST GAS, RECIRCULAT- ING MEANS FOR RELIEF F PULSATIONS Gordon J. Fairbanks, Indianapolis, Ind., assignor to Stewart-Warner Corporation, Chicago, Ill., a corporation of Virginia Application August 29, 1950, Serial No. 182,021

3 Claims. (Cl. 15S- 1) The present invention relates to improvements in in ternal combusion heaters of the sealed combustion cham ber type to improve their operating and fuel burning characteristics particularly when such heaters are equipped with long exhaust pipes. A typical sealed combustion chamber heater is disclosed in United States Letters Patent No. 2,507,081 issued May 9, 1950.

This application is a continuation in part of the copending application of Gordon J. Fairbanks, Serial No. 682,940, tiled July ll, 1946, now abandoned.

Certain types of combustion heaters, particularly those in which the combustion chamber is sealed so that the products of combustion are carried from the heater to the atmosphere through a long exhaust pipe without the possibility of contaminating the surrounding air, have the unfortunate characteristic of rough running. Such rough running causes ineicient combustion and under some conditions may cause the combustion to become so unstable as to be unreliable. It has been found that, as a general rule, the longer the exhaust pipe the greater the roughness in the heater combustion, so that it has been proposed in some instances to install heaters of the sealed combustion chamber type only under conditions where a comparatively short exhaust would lead to the outside atmosphere. The disadvantages of such a scheme are apparent and are overcome by the present invention.

The rough running in a sealed combustion type of heater is caused by pulsations in the burning gases which occur regularly and rapidly though at diiferent rates or frequencies for heaters of different designs and sizes. These pulsations are very likely caused by the rapid intermittent expansion of the burning gases. If the heater has substantially no resistance or back pressure at its exhaust outlet, this expansion takes place in the direction of low resistance, namely toward the exhaust. However, when the heater is itted with a long exhaust pipe of perhaps eight or ten feet, a long air or exhaust gas column must be moved by the burning gases. Since the gas column in the exhaust pipe or system oifers a very great resistance or inertia to the sudden expansion of burning gases in the exhaust direction, at least a part of this expansion causes a rapid rise in pressure at the combustion air inlet. Since the air for combustion is being fed under pressure, it eventually overcomes the momentary burning gas expansion toward the inlet and the whole mass ultimately moves toward the exhaust outlet. However, the momentary break in the constant and even ow of air for combination slows down the burning in the combustion chamber due to somewhat less than adequate combustion air. Thus a momentary condition of low pressure follows a period of high pressure in the combustion chamber, which in turn will be rapidly followed by a renewed rapid burning of gases and an expansion thereof to repeat the cycle. 1t appears that more or less rapldly alternating high and low pressure conditions are present in the combustion chamber. These high and low pressures cause fluctuations in the ratio of fuel and combustion air, and consequently in the rate of combustion. It will be appreciated that these fluctuations in ratio and rate have an adverse effect on combustion and under some extreme conditions will quench it.

It is, therefore, the object of the present invention to provide a novel combustion heater of the sealed combustion chamber type having means to prevent rough running or pulsations in combustion.

Another object is to provide a novel combustion heater vopposite the exhaust spud 34 latented Jan. 18, 1955 of the sealed combustion chamber type: which may have an exhaust pipe of any convenient length and yet does not possess the disadvantages in pulsating combustion normally attendant upon long exhaust pipes.

Another object is to provide a novel combustion heater wherein the exhaust gases are at least partially vented near the exhaust end of the heater and in such manner as not to contaminate the surrounding air.

Another object is to provide a novel combustion heater wherein a fraction of the heater exhaust gases are recirculated with fresh air for combustion..

Still another object is to provide an exhaust system for an internal combustion heater having a long exhaust pipe wherein a minor portion of the products of combustion are vented immediately adjacent the heater exhaust outlet while the major portion are exhausted at a point remote from the heater. i

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawings, wherein:

Fig. l is an elevational view, partially broken into section, of a preferred form of internal combustion heater incorporating the present invention;

Fig. 2 is an elevational View, partially broken in section, of the heater of Fig. 1 taken from the right or exhaust end of the heater; and

Fig. 3 is a fragmentary sectional View taken along the lines 3-3 of Fig. 1, looking in the direction of the arrows.

Referring to the drawing, the reference character 10 indicates generally a heater of the general type disclosed inthe aforementioned United States Letters Patent No. 2,507,081, and includes an outer casing 12 enclosing a burner 14 and a heat exchanger 16. Air for combustion is supplied by a blower 1S driven by motor 20 to deliver air through a duct 22, tting 24, and conduit 2S Within the heater to the burner 14. Fuel in a liquid state is supplied through a control valve 26 and conduit 28 to a chamber or pocket 30 which also encloses an igniter 32 of suitable type. The control valve 26 may be of any convenient type which is for the purpose of turning the heater off and on and under some conditions may also operate to modulate the heat output between high and low position.

From the heat exchanger the products of combustion ow through an exhaust spud 34 to which is secured an exhaust pipe 36 by means of sheet metal screws or the like 3S. Air for ventilation is supplied to the heater casing 12 from a blower 39 driven by motor 41. The heater may be equipped with any suitable control system for turning the heater on and off in response to temperature conditions within the space to be heated and in response to combustion detection and overheat conditions in the heater. Such controls have not been illustrated inasmuch as they form no part of the present invention.

The heat exchanger 16 includes three generally concentric shells 42, 43 and 44. The inner shell 42, which is closed at the right end by a panel 46 and at the left end by the burner structure 14 defines primarily the combustion chamber. Air to be heated is forced longitudinally of the heater between the shells 42 and 43 and between shell 44 and casing 12 by the blower 39. The space enclosed by the shells 43 and 44 constitutes a path forthe flow of the products of combustion which are received from the combustion chamber through a slotted opening 50 in the shells 42 and 43 and extending a substantial distance longitudinally of the heater. The shell 43 is offset inwardly at 49 at both sides and the ends of the slot to bear against the shell 42 to which it is electrically seam welded to form a gas-tight joint. The slot 50 is diametrically so that the exhaust gases will be forced in two paths in the annular space between the shells 43 and 44 to the exhaust opening. This annular space is closed at either end of the heater by metal rings 45 welded to the shells 43 and 44. Opposite the slot 50 and adjacent the exhaust spud 34, the shells 42 and 43 are formed with abutting spacing bosses 48, and the casing 12 is properly supported around the shell 44 by a plurality of spacers 47.

:The exhaust Spud 34 is secured to the shell 44 at a pomt approximately midway of the heat exchanger structure 16. Immediately adjacent the spud 34 is a second ror venting spud 52 connected to the shell 44 which projects outside the heater casing 12 to vent products of combustion from the space between the shells 43 and 44. The blower `18 is provided with an inlet casing 54 of elongated shape Vwhich extends from the center of the blower to a point opposite the auxiliary or venting exhaust spud 52. The inlet to the casing 54 comprises a generally cylindrical shell 56 which extends toward the heater casing 12 and terminates at a point adjacent thereto but spaced therefrom and in such position as to surround the outlet from the spud 52. Exhaust gases expelled through the exhaust outlet 52 are dumped into the inlet to the blower 18, and are recirculated with fresh combustion air drawn in as indicated bythe arrows in Fig. 3 to the inlet of the blower 18.

Theheater operates in the following manner: `Cornbustion is initiated in the combustion chamber and burner 14 in the customary fashion by the igniter 32, and fuel is continuously fed to the burner through the fuel metering valve 26 and pocket 30. Air for combustion is supplied by the blower 18 through the conduit 22, fitting 24 and heater conduit to the'burner 14 where it picks up fuel from a pool lying in the bottom of the burner well to form a combustible mixture. Once the combustion is established in the combustion chamber, the products of combustion circulate from the combustion chamber through the slot 50 and between the shells 43 and 44 to reach the exhaust spuds34 and 52. The major portion of the exhaust is expelled through the outlet 34 and exhaust pipe 36, and is exhausted to the atmosphere at some convenient and perhaps remote place from the heater. The heater thus far described is that shown in the aforementioned Patent No. 2,507,081, which has proved to be quite satisfactory, but under some conditions when equipped with a relatively long exhaust pipe or an exhaust system creating 'excessive back pressure or inert1a it 1s subject to the disadvantages discussed in the opening n paragraph of this specification.

It is to be noted, however, that with the provision of the exhaust spud 52 at a point closely adjacent the exhaust outlet 34 a portion of the exhaust gases is expelled from the heater immediately adjacent theexhaust outlet. otherwise bebuilt up vagainst the column of air and gases in the exhaust pipe 36. Fluctuations and expansions in the products of combustion arising in the burning gases in'the combustion chamber are relieved and compensated through the exhaust spud 52` where no substantial back pressure or inertia is experienced.

In order to dispose of these gases without contaminating the air immediately surrounding the heater 10, these exhaust gases are dumped into the inlet to the combustion air blower 18 and are then recirculated to the burner 14. It has been found as a matter of practical experience that the introduction of a small fraction of exhaust gases into the combustion air inlet does not deleteriously affect combustion or heater operation. It is, therefore, seen that the disadvantages usually attendant upon the use of a relatively long exhaust pipe to convey the products of combustion to a convenient place in the atmosphere have vbeen completely overcome by the provision of the secondary exhaust outlet S2 which introduces a portion of the products of combustion into the inlet of the combustion air blower.

Having described a preferred embodiment of the invention, it will become apparent to those skilled in the art that numerous modifications and changes may be made without departing from the spirit of this invention which 'This relieves the back pressure which would bustion from the heatexchanger portion of the structure, and an exhaust pipe connected to the exhaust connection and extending a substantial distance therefrom to a remote point, the improvement comprising projecting means forming an unobstructed vent opening in the combustion chamber and heat exchanger forming structure immediately adjacent said exhaust connection for venting at least a portion of the products of combustion to the atmosphere to relieve pressure pulsations in the burning gases in' the combustion chamber and to prevent such pulsations from being communicated to the products of combustion in the exhaust pipe, and conduit means having one end adapted to be connected to the inlet to the combustion air blower and an open end into which said vent opening forming means projects in spaced relation thereto so that the vented products of combustion may be conducted to the combustion air blower for recirculation with fresh combustion air.

V2. An internal combustion heater including in combination a structure forming a sealed combustion chamber and heatexchanger, a casing enclosing the structure, a blower for supplying combustion air to the combustion chamber, anexhaust connection from the heat exchanger portion of. the structure, and an exhaust pipe connected to the exhaust connection to receive and carry away the products of combustion, characterized by an open ended and unobstructed vent connection extending outwardly from the heat exchanger portion of the structure through the casing, said vent connection being positioned closely adjacent the exhaust connection to vent the products of combustion to relieve pressure pulsations in the burning gases in the combustionchamber and to prevent such pulsations from being communicated to the products of combustion in the exhaust pipe, and an inlet casing for the combustion air blower, said inlet casing having means formlngan inlet opening encompassing and spaced from the open end of said vent connection to receive the vented products of combustion for recirculation to the combustion chamber with fresh combustion air.

3. An internal combustion heater including in combination a structure forming a sealed combustion chamber and heat exchanger, a casing enclosing the structure, a blower for supplying combustion air to the combustion chamber, and an exhaust system connected to the heat exchanger portion of the structure to receive and carry away the major portion of the products of combustion, characterized by a short open ended Vandv unobstructed ventconduit connected to the heat exchanger portion'of the structure adjacent the connection of the exhaust system to .the structure and projecting outwardly through the casing to vent a minor portion of the products of combustion to a point of pressure lower than that in the exhaust system to relieve pressure pulsations in the burnlng gases in the combustion chamber and to prevent such .pulsations from being communicated to the products of combustion in the exhaust system, and an inlet casing for the combustion air blower, said inlet casing having an inlet opening into which the open end of said vent conduit projects in spaced relation thereto, whereby the vented vminor portion of the products of combustion is recirculated with fresh air.

References Cited in the le of this patent UNITED STATES PATENTS 1,076,494 Galaine Oct. 21, 1913 1,487,312 Bull Mar. 18, 1924 1,684,991 Inglis Sept. 18, 1928 1,702,936 Frenier Feb. 19, 1929 1,738,881 Frcnier Dec. 10, 1929 1,954,516 Bourne Apr. 10, 1934 2,078,884 Vollmer Apr. 27, 1937 2,086,812 Luty July 13, 1937 2,174,663 Keller Oct. 3, 1939 2,514,520 ASauer July 11, 1950 2,517,446

Ryder et al. Aug. l, 1950 

